Current collector assembly for small d. c. motors



y June 22, 1955 HlRosHl ooKA ETAL. 3,191,034

CURRENT COLLECTOR ASSEMBLY FOR SMALL D.C. MOTORS Filed Nov. 20, 1962 Fig. 3

46 46 nVEmDRS Hiroshi OoKa.. Kazuo Oh'lh'l ATTOFnEy United States Patent O 3,191,034 QURRENT CLLECTOR ASSEMBLY FOR SMALL BeC. MTORS Hiroshi Goka, Kazuo Gnislii, and Shuzo Oshima, Hitachishi, Japan, assignors to Hitachi, Ltd., Tokyo, Japan, a corporation of .tapan lliied. Nov. 20, 1962, Ser. No. 238,910 `Ciaims priority, application Japan, Nov. 22, 1961, 36/41,768, StG/41,769 6 Claims. (Cl. S10-219) Micromotors of extremely miniature size are presently in use with various kinds of automatic control devices and miniature tape-recorders. Because of their limited sizes, commutator devices for such micromotors are required to be. very limited in losses, simple in structure, easy to fabricate, and serviceable yfor extended life periods. In

`the past, however, because of the use of silver-copper alloys, Phosphor bronzes and similar alloys, commutator devices for micromotors have been usable only for limited periods of use since the brushes and commutator have been susceptible to wear and deterioration due to sparking.

Attempts have long been made to use lilamentary brushes with a micromotor because such a construction simplifies the brush structure and reduces friction loss; however, a difficulty met in the use of such lamentary brushes in the commutator device for a micromotor is rapid deterioration of the commutator and brushes due to wear. This make the commutator device unusable after only a limited period of use. Accordingly, such a commutator device has been employed only in motors such as used with toys and has not been used in micromotors which are required to have an extended service life.

It is evident that the ilamentary brushes for a micromotor should be made as fine as possible and used with a reduced contact pressure if only for the purpose of reducing friction loss. Actually, however, relatively thick brushes have been used in consideration of the frictional wear of the brushes and their deterioration due to sparking, making the loss due to friction between the commutator and brushes suiciently substantial to adversely aifect the performance of the device. Moreover, with micromotors, the commutator device is very limited in size, making the preparation of the brushes and commutator extremely diicult. Particularly, the so-called undercutting operation, in which the insulation between the adjacent commutator segments is shaved down below the peripheral surface of the commutator, is not only extremely difficult to carry out but is undesirable since the axial grooves formed in the commutator surface by such undercutting operation causes unwanted vibration of the brushes held in sliding contact with the comrnutator4 surface. ln the prior art, however, the undercutting operation upon the commutator assembly has been indispensabie since without such operation the insulators between the commutator segments would remain ush with the latter forming the peripheral surface of the comniutator with the result that in case the commutator cornes to rest with the brushes positioned upon such commutator insulators the motor can no longer start by itself.

The present invention is intended to eliminate the above diiiculties met with in conventional commutator devices for micrornotors.

The primary object of the present invention is to provide an improved commutator device for a micromotor including a conimutator and brushes both having irnproved wear-resisting and spark-resisting characteristics by forming the commutator segments of a silver-palladium alloy consisting essentially of 80% to 60% silver and 20% to 40% palladium and the brushes of a platinumiridium alloy consisting essentially of 95% to 70% platinum and to 30% iridium considering the wear of ,p 3,191,084 Patented June 22, 1965 ICC the commutator and brushes due to friction therebetween.

Another object of the present invention is to attain the same result as indicated in the preceding paragraph by forming the commutator segments of a silver-palladium alloy consisting essentially of 80% to 60% silver and 20% to 40% palladium and the brush conductors of an alloy consisting essentially of to 80% gold, 5% to 20% platinum and 10% to 15% copper.

A further object of the invention is to provide brushes which are highly flexible and thus capable of accommodating any vibration of the commutator by forming the brushes of a suitable filamentary conducting material of 0.05 to 0.25 millimeters in diameter.

A still further object of the present invention is to provide a commutator device including a commutator which requires no undercutting` of insulator and is free from trouble previously incurred when the undercutting operation was omitted. To this end, according to the present invention, the commutator device employs conducting brushes each having brush conductors arranged to Contact with the commutator at points thereon circumferentially spaced from each other.

Other objects, features and advantages of the present invention will become apparent from the following description when take in conjuction with the accompanying drawing, which illustrates a preferred embodiment of the invention and in which:

FIG. 1 is a front elevation, partly in section, of a micromotor having a commutator device embodying the present invention;

FG. 2 is a cross-sectional view taken along 2--2 in FIG. l; and

FIG. 3 is a circuit diagram of the micromotor.

In the drawing, there is shown a micromotor having a cylindrical housing 1 in which an annular stator 2 is arranged in fixed relation thereto. An armature or rotor 3 is mounted fast on a rotor shaft 4 within the stator 2 and has :slots with the armature windings 5 received therein. Lead wires 6 extending from the armature windings 5 are connected to the risers 8 of the commutator 7 of the motor. The commutator 7 according to the present invention includes commutator segments 9 made of an alloy consisting essentially of silver and 30% palladium and arranged radially about the rotary shaft 4 by way of an insulator 1d. A brush mounting 11 of insulating material is annular in :shape and fitted in the housing 1 with metallic brush holders 13 tix-ed to one side face of the brush mounting 11 by screws 12 on dametrally opposite sides of the commutator 7. Formed on each of the brush holders 13 is a lug 14 to which two line iilamentary brush elements 15 and 16 are welded so as to be held in contact wtih the commutator tangentially thereto at angularly :spaced points thereon.

With this embodiment, the brush elements 15 and 16 each take the form of a lilament of 0.1 millimeter diameter made of an alloy consisting essentially of platinum and 20% iridium and having a Vickers hardness of approximately 270. The brush mounting 11 is firmly held in place by screws 18, which are each insulated with respect to the housing 1 by an insulating bushing 17 and can be tightened externally. The screws 18 are electrically connected with the respective screws 12 securing the metallic brush holders 13 to the brush mounting 11 to serve as terminals for the respective brushes.

The housing 1 is formed adjacent to one end and in the inner wall thereof an annular recess 20, which receives an annular abutment 21. A circular disc 22 is fitted in the housing inwardly of said abutment ring 21 and is bored to receive threaded bolts 23, which extend through an end bracket 19 to clamp the end bracket and the disc against the respective sides of the annular abutment. A

the une onerose ball bearing 24 is arranged between the end bracket 19 and the rotary shaft 4 as illustrated. An oil slinger Z6 is mounted on the rotary shaft on that side ofthe circular disc 22 remote from the ball bearing 24 to cooperate with the hub portion 25 of the disc 22. The rotary shaft 4 extends outwardly beyond the ball bearing 24 and carries another oil slinger 27.

A governor disc 2S is mounted on the rotary shaft 4 at its extended end and includes an axially extended boss which carries at its extreme end a central electrode 29, which in turn carries an insulated slip ring 36 about its periphery. A weighted mass 31 is mounted on the governor disc 28 by way of a resilient arm carrying a movable contact 32. A fixed contact 33 is arranged opposite to the movable contact 32. The movable and xed contacts are electrically connected to the central electrode 29 and the slip ring 30, respectively, to cooperate with each other. It is to be understood that in operation the weighted mass 31 is movable radially outwardly under the centrifugal force acting thereon. A governor casing 34 is titted over the motor housing 1 at the adjacent end lthereof as shown. Fitted in the casing 34 adjacent to the central electrode 29 and slip ring 30 is an insulating mounting ring 35 in which two cylindrical electroconductive inserts 37 are anchored to extend through the thickness of the ring 35 in diametrally opposite relation to each other. formed with a threaded through holev 3:6. A brush holder 38 is secured to one side of the mounting ring 35 by a screw 39 threadably tted in the hole 36 in one of the electroconductive inserts 57. Brush elements 40 are welded to the brush holder 3S and held in contact with the slip ring 30. A resilient strap 42, which is electroconductive, is fixed to the other side of the mounting ring 35 my means of a screw 43 fitted in the other eleetroconductive insert 37 -and carries an electric contact 44, which is held in alignment and contact with the central electrode 29 under the resilience of the strap 42.

The insulating mounting ring 35 is firmly secured to the governor casing 34 by bolts 46, which are each insulated therefrom by an insulating bushing 45 and positioned in contact with the adjacent electroconductive insert 37 to serve as an outlet terminal.

Another end bracket 47 is fitted to the motor housing at the opposite end thereof and mounted on the rotary shaft 4 by way of a ball bearing 48. The motor housing 1 also is annularly recessed adjacent the opposite end as at 49 to receive an annular abutment 50. An annular disc 51 is fitted in the housing axially inside of the annular abutment S and bored to receive threaded bolts 52, which extend through the end bracket 47 Vto clamp the latter against the end face of the housing 1.

The wiring of the micromotor illustrated will now be described with reference to the circuit diagram of PEG. 3.

One of the screws 18, which hold the brush mounting 11 in place and serve as outlet terminals, is connected to a supply line 53 leading to a direct-current power source while the other screw 18 is connected to one of t te bolts 46 and by way of a resistance 54 of approximately 300 ohms to the other bolt 46, whichV is connected to another supply line 55. Y

With micromotors constructed and arranged as described above, it is noted that the commutator device is most influential upon the performance and service life of the micromotor. Accordin I to the present invention, the commutator 7 is formed with a complete cylindrical peripheral surface having no undercut grooves so as to prevent the brush elements from jumping. The elimination of the undercutting operation in the manufacture of commutators has been Vmade possible by the arrangement of brush elements and 1d in which these ele-V ments are welded to the lug 14 of the metallic brush holders 13 at angularly spaced-apart points to extend tangentially to the commutator 7 in different directions, and thus is held in contact with the coinmutator 74 at more The electroconductive inserts 57 are each or less angularly spaced-apart points on the periphery thereof. As will be appreciated, with this arrangement the supply of current to the armature windings 5 will never be completely interrupted even when one of the brush elements cornes to contact with the commutator at the top of the insulation between the commutator segments 9 as the other brush element then contacts with one of the commutator segments.

The combination of the material of which the commutator segments 9 are made and the material of the brush elements 15 and 16 is an extremely important factor relative to the life of the commutator device. With the embodiment illustrated, a life of 4000hours or over has been obtained by employing an alloy consisting essentially of 70% silver'and 30% palladium for the cornmutator segments 9 and an alloy consisting essentially of 80% platinum and 20% iridium for the brush elements 15 and 16, as indicate-d above. To guarantee such life of service, it has been found that the alloy for the commutator segments 9 should consist essentially of 80% to 60% silver and 20% to 40% palladium and the alloy for the brush elements 15 and 1d should contain 95% to platinum and 5% to 30% iridium.

lt has also been found that similar results may be obtained by employing an alloy consisting essentially of 50% to 80% gold, 5% to 20%V platinum, 10% to 15% copper and the rest of a few percent for brush elements 15 and 1d. For example, a service life of 4000 hours or over has been obtained by employing a commutator 7 including commutator segments 9 made of an alloy consisting essentially of 70% silver and 30% palladium and brush elements 15 and 1d of 0.1 millimeter diameter made of an alloy commercially available under the trade name of Fallini, which consists of 58% gold, 16% platinum, 9% silver, 12% copper, 4% palladium, and 1% Zinc. It is true that the life of the commutator device depends more or less upon the Contact pressure between the commutator and the brushes as well as upon the diameter of each of the brush elements 15, 1d, but the most important factor in this connection is the'combination in which the materials for Vthe commutator and the brushes are used. it has been found that, if the'same materials be employed in a combination opposite to that described above in connection with the embodiment illustrated, the service life obtained would be extremely limited, making the use of such materials substantially meaningless.

, The contact pressure between the commutator and the brushes, one of the factors affecting the life of the cornmutator device for micromotors, also affects the current supply to the armature windings 5. Reduction in the contact pressure of the brush elements 15 and 16 is advantageous as far as the mechanical loss due to friction between the commutator and the brushes is concerned. The situation, however, is reversed when viewed from the standpointof the'electrical resistance. Under these circumstances, a compromise is usually made with this problem in regard to the friction loss and the electrical resistance between the commutatcr Iand the brushes. in practice, the commutator is vibrated if not to any substantial extent as it rotated. In addition, the amount of deilecion of the brush elements 15 and 16 gradually varies to affect the contact'pressure between the commutator 7 and the brush as the commutator is worn. In order to minimize suchdeleterious effects, the brush elements 15 and 16 are required to 'have a satisfactory flexibility. This problem of the flexibility of brushes might be solved by reducing the diameter of the brush elements 15V and 16 to an extreme extent, but to do this would obviously result in a very limited service life of the brushes. It has been found that, with the inventive commutator device employing the combination of alloys :as described hereinbefore, a contact pressure of from 0.5 to 3.0 grams is preferable to provide a satisfactory power supply to the armature windings 5 through the contact between the commutator segments 9 and the brush elements 15, 16. With such contact pressure, a satisfactory exibility can be obtained with the brush by employing brush elements and 16 each taking the form of a filament having a diameter of 0.05 to 0.25 millimeter. The contact pressure of 0.5 to 3.0 grams may generally be obtained by employing an increased amount of deflection of the filaments even when they are made thin enough to have a satisfactory flexibility. However, such thin lamentary brush elements cannot be used for any extended period of time because of the heavy wear to which the iilaments are subjected. It is to be appreciated that the use of brush elements 15 and 16 having a diameter as small as 0.05 to 0.25 millimeter can be realized only by use ofthe combination of materials according to the present invention.

It will be appreciated from the foregoing that the present invention oiers several important advantages such as the substantial reduction in size, extreme ease to manufacture and extended life of service to commutator devices for micromotors, which are required to meet exacting conditions in fabrication as Well as in operation.

The invention is not restricted to the features described above and shown in the drawing but may be varied in many Ways within the scope of the appendant claims.

What is claimed is:

1. A commutator device for a micromotor comprising a commutator on the rotor shaft of the micromotor including commutator segments made of a silver-palladium alloy consisting essentially of 80% to 60% silver and to 40% palladium, and metallic brush holders ixedly arranged about the commutator and each carrying a brush made 4of a platinum-iridium alloy consisting essentially of 95% to 70% platinum and 5% to 30% iridium in a manner so that the brush is held in sliding contact with the commutator,

2. A commutator device for a micromotor comprising a commutator on the rotor shaft of the micromotor including commutator segments made of a silver-palladium alloy consisting essentially of 80% to 60% silver and 20% to 40% palladium, and metallic brush holders iixedly arranged about the commutator and each carrying a brush made of an alloy consisting essentially of 50% 80% gold, 5% to 20% platinum and 10% to 15% copper,

said brush being held by its associated holder in sliding contact with the commutator.

3. A commu-tator device for a micromotor comprising a commutator including an array of commutator segments arranged on the rotor shaft of the micromotor in insulated relation to the rotor shaft, and metallic brush holders each carrying at least one brush element in sliding contact with the commutator, said brush element taking the form of a filament having a diameter of 0.05 to 0.25 millimeter and made of an alloy consisting essentially of 80% to 60% silver and 20% to 40% iridium.

4. A commutator device for a micromotor comprising a commutator including an array of commutator segments arranged on the rotor shaft of the micromotor in insulated relation to the rotor shaft, and metallic brush holders each carrying at least one brush element in sliding contact with the commutator, said brush element taking the form -of a lament having a diameter of 0.05 to 0.25 millimeter and made of an alloy consisting essentially of to 80% gold, 5% to 20% platinum, 10% to 15% copper.

5. A commutator device for a micromotor comprising a commutator including an array of commutator segments arranged on the rotor lshaft of the micromotor in insulated relation to the rotor shaft, and ilame-ntary brush elements each having a diameter of 0.05 -to 0.25 millimeter and held in contact with the commutator at a contact pressure of 0.5 to 3.0 grams.

6. A commutator device for a micromotor comprising a commutator including an array of commutator segments arranged on the rotor shaft of the micromotor in insulated relation to the rotor shaft, and metallic brush holders each carrying at least one brush element in sliding contact with the commutator, said brush element taking the form of a lament having a diameter of 0.05 to 0.25 mm. and made `0i au alloy consisting essentially of 50% to 80% gold, 5% to 20% platinum, 10% to 15% copper, 1% to 9% silver, and 1% to 9% palladium.

References Cited by the Examiner FOREIGN PATENTS 1,098,618 3/55 France. MILTON O. HIRSHFIELD, Primary Examiner. 

1. A COMMUTATOR DEVICE FOR A MICROMOTOR COMPRISING A COMMUTATOR ON THE ROTOR SHAFT OF THE MICROMOTOR INCLUDING COMMUTATOR SEGMENTS MADE OF A SILVER-PALLADIUM ALLOY CONSISTING ESSENTIALLY OF 80% TO 60% SILVER AND 20% TO 40% PALLADIUM, AND METALLIC BRUSH HOLDERS FIXEDLY ARRANGED ABOUT THE COMMUTATOR AND EACH CARRYING A BRUSH MADE OF A PLATINUM-IRIDIUM ALLOY CONSISTING ESSENTIALLY OF 95% TO 70% PLATINUM AND 5% TO 30% IRIDIUM IN A MANNER SO THAT THE BRUSH IS HELD IN SLIDING CONTACT WITH THE COMMUTATOR. 